1. Field of the Invention
The present invention relates to a liquid discharge head and a liquid discharge apparatus that discharge a desired liquid by generation of a bubble due to thermal energy or the like, and more particularly, to a liquid discharge head and a liquid discharge apparatus having a movable member which is displaced by the use of generation of the bubble.
The term xe2x80x9crecordingxe2x80x9d in the present invention means to attach not only an image such as a character and a figure having a meaning but also an image such as a pattern to a recording medium.
2. Description of the Related Art
Conventionally, in a recording apparatus such as a printer, an ink-jet recording method, a so-called bubble-jet recording method, has been known, in which energy such as heat is given to a liquid ink in a flow path to generate a bubble, ink is discharged from discharge part by an effort based on a steep volume change with the generation of the bubble, and the ink is adhered to the recording medium to form an image. In the recording apparatus using the bubble-jet recording method, a discharge part for discharging ink, a flow path communicating with the discharge part, and an electro-thermal converter as energy generation means for discharging ink provided in the flow path are generally provided, as disclosed in the U.S. Pat. No. 4,723,129.
According to such a recording method, a high-resolution image can be recorded in a high-speed and with a low noise, and the discharge part for discharging ink can be arranged in a high density in a head performing the recording method. Therefore, the recording method has many superior aspects that a recorded image or a color image of a high-resolution can be easily obtained by a small apparatus. Thus, the bubble-jet recording method has been used in various office appliances such as a printer, a copier and a facsimile, and furthermore, it has also been used in an industrial system such as a textile printing apparatus.
As bubble-jet technology has been used in products of various directions, the followings have been requested in recent years.
To obtain a high image quality, drive conditions are suggested by which a liquid discharge method and the like having a high discharge speed of ink and capable of performing good ink discharge based on stable bubble generation has been provided. In addition, from the viewpoint of high-speed recording, a recording method has been suggested in which the shape of the flow path is improved to obtain a liquid discharge head having a high filling (refilling) speed of a discharged liquid into the liquid flow path.
Other than the head described above, an invention having a construction to prevent a back wave being loss energy during discharge is disclosed in Japanese Patent Application Laid-Open No 6-31918, which pays attention to the back wave (a pressure directed to a direction opposite to the direction toward the discharge part) generated with generation of the bubble. The invention described in the gazette is one that a triangular portion of a triangular plate member is arranged opposing to a heater that generates the bubble. In the invention, the back wave is temporarily controlled by a little amount by the plate member. However, since the invention does not mention a relative relation between the growth of the bubble and the triangular portion nor has such conception, the invention has the following problem.
Specifically, in the invention described in the gazette, an ink droplet shape cannot be stable because the heater is positioned at the bottom of a concave portion and cannot have a communication state in-line with the discharge part. Moreover, since the growth of the bubble is permitted from the periphery of the apex portion of a triangle, the bubble grows from one side of the triangular plate member entirely to the opposite side. Accordingly, normal growth of the bubble in the liquid completes as if the plate member does not exist. Therefore, existence of the plate member is not effective to the bubble that has grown. On the contrary, refill to the heater being positioned at the concave portion causes a turbulent flow in a contraction step of the bubble because the entire plate member is surrounded by the bubble, which causes micro bubbles to accumulate in the concave portion and breaks the principle where discharge is performed based on a growing bubble.
Moreover, the European Patent Publication No. 436047A1 suggests an invention that alternately opens/closes a first valve and a second valve, the first valve blocking the vicinity of the discharge part and a bubble generation section between them and the second valve completely blocking the bubble generation section and an ink supply section between them (refer to FIG. 4 to FIG. 9 of the gazette). However, in the invention, the three chambers are severally divided in two divisions, ink following the liquid droplet tails long during discharge, and thus considerably more satellite dots are produced compared to a normal discharge method where bubble growth, contraction, and bubble disappearance are performed (thus, it is presumed that effect of meniscus withdrawal due to the bubble disappearance cannot be used). Further, although the liquid is supplied to the bubble generation section with the bubble disappearance during refilling, the liquid cannot be supplied to the vicinity of the discharge part until the next bubble growth begins. Accordingly, not only dispersion of the discharged liquid droplets is large, but also discharge response frequency is extremely small, which are not in practical levels.
On the other hand, a number of inventions using a movable member (a plate member or the like having a free end closer to the discharge part side from a fulcrum) that effectively contributes to liquid droplet discharge are suggested by the inventors, which are totally different from the prior art. Among others, Japanese Patent Application Laid-Open 9-48127 discloses an invention that defines an upper limit of a displacement of the movable member in order to prevent the action of the foregoing movable member from being troubled. In addition, Japanese Patent Laid-Open No. 9-323420 discloses an invention in which the position of a common liquid chamber in an upstream to the above-described movable member is shifted closer to the free end side of the movable member, that is, to a downstream side utilizing the advantage of the movable member. As a presumption for creating the inventions, the inventors adopted a mode that the growth of the bubble is suddenly released to the discharge part side from a state of temporarily wrapping the bubble by the movable member. Accordingly, no attention is paid to individual element of the whole bubble regarding the formation of the liquid droplet and the relative relation thereof.
As the next step, the inventors disclose an invention in Japanese Patent Application Laid-Open 10-24588 that a portion of a bubble generation region is released from the above-described movable member, which is an invention (an acoustic wave) where its attention is paid to the bubble growth by pressure wave propagation as an element regarding the liquid discharge. However, since the invention also pays attention only to the growth of the bubble during the liquid discharge, no attention is paid to individual element of the whole bubble regarding the formation of the liquid droplet and the relative relation thereof.
Despite that the front portion (an edge shooter type) of a bubble by a film boiling, which has been conventionally known, greatly influences the discharge, no invention has paid attention to this conventionally for contributing to the formation of the discharged liquid droplet more effectively. The inventors have researched this with much effort for technical resolution.
Furthermore, the inventors have obtained the following effective finding when they paid attention to the displacement of the movable member and the generated bubble.
The finding is that the displacement of the free end of the movable member to the growth of the bubble is defined (restricted) by a restricting portion (a stopper). By restricting the displacement of the movable member by the restricting portion, the growth of the bubble in the upstream of the flow path is defined, and thus energy propagates for effectively discharging the liquid toward the downstream side where the discharge part is formed.
In the liquid discharge head having the foregoing constitution, there has been a case where dissolved gas in the liquid becomes a remained bubble due to change by passage of time, temperature increase by continuous bubble growth, and the like. Specifically, the bubble generated in the flow path due to change by passage of time, temperature increase by continuous bubble growth, and the like tends to be left in the front and rear of the restricting portion. Particularly, there is a portion where the liquid is hard to flow and stagnate in the vicinity of the restricting portion, and there has been a case when the bubble is left fixedly in the portion. In the following description, such a bubble is referred to as the remained bubble, which is distinguished from the bubble for liquid discharge that is grown by heat and disappeared. If the remained bubble is left fixedly in the front and rear of the restricting portion, deterioration of printing may have been caused because a bubble foaming power was absorbed by the remained bubble to reduce a discharge amount and a discharge speed or a discharge direction became unstable.
Specifically, as shown in FIG. 17A, if a remained bubble 450 exists in the vicinity of a restricting portion 412, the liquid discharge operation shown in FIG. 17B and FIG. 17C, and then the remained bubble 450 does not move and becomes residual even if the refill (refilling of the liquid) is performed as shown in FIG. 17D. This is because the flow of the liquid progresses so as to avoid the vicinity of the restricting portion 412, little flow of the liquid is made in the vicinity of the restricting portion 412, and the remained bubble 450 is also left in the portion without being washed down. As described, when the remained bubble 450 is left in the position, a bubble foaming pressure during bubble generation by heating of a heat generator 410 as shown in FIG. 17E to FIG. 17G is absorbed by the remained bubble residual in the portion, which leads to insufficient liquid discharge.
The object of the present invention is to prevent the remained bubble from being left in the vicinity of the restricting portion and also to prevent reduction of the liquid discharge performance due to a residual remained bubble.
The present invention is a liquid discharge head that comprises: a heat generator that generates a thermal energy for generating a bubble in a liquid; an discharge part as portions to discharge the liquid; a flow path communicating with the discharge part and having a bubble generation region in which the bubble is generated; a movable member having a free end and is displaced with the growth of the bubble; and a restricting portion to define (restrict) a displacement amount of the movable member, in which the flow path is formed by joining a substantially flat substrate provided with the heat generator and the movable member and a top plate opposing to the substrate and including the restricting portion, and the liquid is discharged from the discharge part by an energy during generation of the bubble, characterized in that the clearance between at least one sidewall of the flow path and the side edge portion of the restricting portion is larger than the clearance between the sidewall and the side edge portion of the movable member.
According to the above constitution, since the liquid can flow through the clearance between the sidewall and the side edge portion of the restricting portion, the foregoing flow of the liquid generated during refilling of the liquid and the like washes down the remained bubble and discharges it from the discharge part even if the remained bubble exists in the vicinity of the restricting portion.
It is preferable that the clearance between the movable member and the restricting portion along the height direction of the flow path, in a non-displacement state of the movable member, is larger than the clearance between the sidewall of the flow path and the side edge portion of the movable member and is smaller than the clearance between the sidewall and the side edge portion of the restricting portion.
Moreover, it is preferable that the sum of the clearance between the movable member and the restricting portion along the height direction of the flow path and the clearance between the movable member and the bottom surface of the flow path, in the non-displacement state of the movable member, is smaller than the clearance between the sidewall and the side edge portion of the restricting portion.
It is also preferable that the distance between the restricting portion and the bottom surface of the flow path in the height direction of the flow path is 15 xcexcm or more, the clearance between the sidewall and the side edge portion of the restricitng portion is 4 xcexcm or more, and the width of the restricting portion is 90% or less of the width of the flow path.
Further, it is preferable that both side edge portions of the restricting portion is convex toward the sidewall and have a shape in which the width continuously becomes narrower from the maximum width portion to the upstream direction and the downstream direction. In this case, the remained bubble moves smoothly along the side edge portion of the restricting portion.
The present invention is also characterized in that the restricting portion is severally formed on the both sidewalls of the flow path, which has a convex shape toward the inside of the flow path, and the clearance between the both restricting portions is larger than the clearance between the sidewall and the side edge portion of the movable member. In such a case, it is preferable that the sidewall has a shape in which the width continuously becomes narrower from the maximum width portion to the upstream direction and the downstream direction.
The liquid discharge apparatus of the present invention includes the liquid discharge head of any one of the foregoing constitutions, and discharges the remained bubble of the dissolved gas in the liquid, which is left in the flow path due to bubble foaming and change by passage of time, during discharge or refilling of the liquid from the discharge part together with the liquid through the clearance between the side edge portion of the restricting portion and the inner wall of the flow path or the clearance between the two restricting portions.
Moreover, the liquid discharge apparatus includes recovery means for recovering the state of the liquid discharge head, and the remained bubble is discharged by the recovery means.
It is to be noted that the terms xe2x80x9cupstreamxe2x80x9d and xe2x80x9cdownstreamxe2x80x9d used in the description of the present invention are expressed as an expression regarding the flow direction of the liquid that directs from a supply source of the liquid toward the discharge part via the bubble generation region (or the movable member), or regarding a constitutional direction.
In addition, the xe2x80x9cdownstream sidexe2x80x9d regarding the bubble itself means the bubble generated in the downstream side relative to the center of the bubble regarding the direction of the flow or the constitutional direction, or the bubble generated in a region downstream side of the area center of the heat generator. In the same manner, the xe2x80x9cupstream sidexe2x80x9d regarding the bubble itself means the bubble generated in the upstream side relative to the center of the bubble regarding the direction of the flow or the constitutional direction, or the bubble generated in a region upstream side of the area center of the heat generator.